The present invention relates to a control system for a device for reproducing the information signal optically recorded on a recording medium.
For instance, in an optical reproduction device available in the prior art, the light beam emitted from a light source is focused on a disk-shaped recording medium (to be referred to as "the recording medium" for brevity in this specification) and is controlled to trace or track a spiral or concentric track produced on the recording medium. The light reflected from or passing through the recording medium is detected by a light sensor. In general, a He-Ne laser or a semiconductor laser is used as such a light source. Audio and/or video signals are recorded on the recording medium in the form of patterns produced by making the surface thereof uneven or light-and-dark image patterns. The recording density is so thick that the signal track is usually about one micron in width and the track pitch is about two microns. Therefore, the light beam must be focused on a small portion having a diameter of about one micron. As a result, a converging or condenser lens having a greater aperture number and a shorter focal length must be used. In addition, the light beam must be so controlled that it is focused correctly on a desired portion of the recording medium. Since the focusing system proper is not included in the subject matter of the present invention, no further description will be presented in this specification.
By means of an optical reproduction device of the type described above, available are various reproduction modes, such as, still picture and slow, quick and/or reverse motions, which will be referred to as "the special effect reproduction modes" in this specification. For the purpose to realize "the special effect reproduction modes" employing such an optical reproduction device available in the prior art, the tracking control system which controls to keep the focused point of the light beam tracing a desired track, is suspended the operation and then some positive and negative rectangular pulses are applied to a tracking element. Thereafter, the tracking control system is caused to resume the operation. In this system, the criteria or the manner of shift or displacement of the light beam depends upon the characteristics or performance of the tracking elements employed so that the width and amplitude of the pulse applied to the tracking element must be adjusted depending upon the characteristics or performance of the element. This adjustment is very troublesome and time-consuming. Furthermore, it is difficult with the prior art system to correctly shift the light beam from one track to another, to skip or jump more than one track. In addition, if a recording track is distorted in pattern because of the eccentricity or some other reasons, and if the pitch between the tracks varies or is irregular, even an ordinary shift or a simple jumping to the adjacent track cannot be realized.